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5 In this question you must show detailed reasoning. Fig. 12 shows part of the graph of \( y=x^{2}+\frac{1}{x^{2}} \). The tangent to the curve \( y=x^{2}+\frac{1}{x^{2}} \) at the point \( \left(2, \frac{17}{4}\right) \) meets the \( x \)-axis at A and meets the \( y \)-axis at B . Ois the origin. Find the exact area of the triangle OAB .

Ask by Cervantes Whittaker. in the United Kingdom
Nov 01,2024

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Answer

The exact area of triangle OAB is \( \frac{169}{120} \).

Solution

To find the area of triangle OAB formed by the origin O, point A where the tangent meets the x-axis, and point B where the tangent meets the y-axis, we will follow these steps: 1. **Find the derivative of the function** to determine the slope of the tangent line at the point \( \left(2, \frac{17}{4}\right) \). 2. **Use the point-slope form of the equation of the tangent line** to find the equations of the lines that meet the axes. 3. **Determine the coordinates of points A and B**. 4. **Calculate the area of triangle OAB** using the coordinates of points O, A, and B. ### Step 1: Find the derivative The function is given by: \[ y = x^2 + \frac{1}{x^2} \] To find the derivative \( y' \): \[ y' = \frac{d}{dx}(x^2) + \frac{d}{dx}\left(\frac{1}{x^2}\right) = 2x - \frac{2}{x^3} \] Now, we evaluate the derivative at \( x = 2 \): \[ y'(2) = 2(2) - \frac{2}{(2)^3} = 4 - \frac{2}{8} = 4 - \frac{1}{4} = \frac{16}{4} - \frac{1}{4} = \frac{15}{4} \] So, the slope of the tangent line at the point \( \left(2, \frac{17}{4}\right) \) is \( \frac{15}{4} \). ### Step 2: Equation of the tangent line Using the point-slope form of the equation of a line: \[ y - y_1 = m(x - x_1) \] where \( (x_1, y_1) = \left(2, \frac{17}{4}\right) \) and \( m = \frac{15}{4} \): \[ y - \frac{17}{4} = \frac{15}{4}(x - 2) \] Multiplying through by 4 to eliminate the fraction: \[ 4y - 17 = 15(x - 2) \] Expanding this: \[ 4y - 17 = 15x - 30 \] Rearranging gives: \[ 4y = 15x - 13 \quad \Rightarrow \quad y = \frac{15}{4}x - \frac{13}{4} \] ### Step 3: Find points A and B **Point A (x-axis intersection)**: Set \( y = 0 \): \[ 0 = \frac{15}{4}x - \frac{13}{4} \] Solving for \( x \): \[ \frac{15}{4}x = \frac{13}{4} \quad \Rightarrow \quad 15x = 13 \quad \Rightarrow \quad x = \frac{13}{15} \] Thus, point A is \( \left(\frac{13}{15}, 0\right) \). **Point B (y-axis intersection)**: Set \( x = 0 \): \[ y = \frac{15}{4}(0) - \frac{13}{4} = -\frac{13}{4} \] Thus, point B is \( \left(0, -\frac{13}{4}\right) \). ### Step 4: Calculate the area of triangle OAB The vertices of triangle OAB are: - O: \( (0, 0) \) - A: \( \left(\frac{13}{15}, 0\right) \) - B: \( \left(0, -\frac{13}{4}\right) \) The area \( A \) of triangle OAB can be calculated using the formula: \[ \text{Area} = \frac{1}{2} \left| x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2) \right| \] Substituting the coordinates: \[ \text{Area} = \frac{1}{2} \left| 0\left(0 + \frac{13}{4}\right) + \frac{13}{15}\left(-\frac{13}{4} - 0\right) + 0\left(0 - 0\right) \right| \] This simplifies to: \[ = \frac{1}{2} \left| \frac{13}{15} \left(-\frac{13}{4}\right) \right| = \frac{1}{2} \cdot \frac{13 \cdot 13}{15 \cdot 4} = \frac{169}{120} \] Thus, the exact area of triangle OAB is: \[ \boxed{\frac{169}{120}} \]

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To find the exact area of triangle OAB formed by the origin O and points A and B where the tangent line meets the x-axis and y-axis respectively, we need to follow these steps: ### Step 1: Find the derivative of \( y \) The function is given by \( y = x^2 + \frac{1}{x^2} \). The derivative is calculated as follows: \[ \frac{dy}{dx} = 2x - \frac{2}{x^3}. \] ### Step 2: Evaluate the derivative at \( x = 2 \) Substituting \( x = 2 \): \[ \frac{dy}{dx} \Big|_{x=2} = 2(2) - \frac{2}{(2)^3} = 4 - \frac{2}{8} = 4 - \frac{1}{4} = \frac{16}{4} - \frac{1}{4} = \frac{15}{4}. \] ### Step 3: Write the equation of the tangent line Using the point-slope form, the equation of the tangent line at the point \( (2, \frac{17}{4}) \) is: \[ y - \frac{17}{4} = \frac{15}{4}(x - 2). \] Rearranging gives: \[ y = \frac{15}{4}x - \frac{30}{4} + \frac{17}{4} = \frac{15}{4}x - \frac{13}{4}. \] ### Step 4: Find the x-intercept (point A) Setting \( y = 0 \) to find \( A \): \[ 0 = \frac{15}{4}x - \frac{13}{4} \implies \frac{15}{4}x = \frac{13}{4} \implies x = \frac{13}{15}. \] So, \( A\left(\frac{13}{15}, 0\right) \). ### Step 5: Find the y-intercept (point B) Setting \( x = 0 \) to find \( B \): \[ y = \frac{15}{4}(0) - \frac{13}{4} = -\frac{13}{4}. \] So, \( B\left(0, -\frac{13}{4}\right) \). ### Step 6: Area of triangle OAB The vertices are \( O(0, 0) \), \( A\left(\frac{13}{15}, 0\right) \), and \( B\left(0, -\frac{13}{4}\right) \). The area \( A \) of triangle OAB can be calculated using the formula: \[ \text{Area} = \frac{1}{2} \left| x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2) \right|. \] Substituting \( O(0, 0) \), \( A\left(\frac{13}{15}, 0\right) \), \( B\left(0, -\frac{13}{4}\right) \): \[ \text{Area} = \frac{1}{2} \left| 0(0 + \frac{13}{4}) + \frac{13}{15}\left(-\frac{13}{4} - 0\right) + 0(0 - 0) \right| = \frac{1}{2} \left| \frac{13}{15} \cdot -\frac{13}{4} \right|. \] Calculating this gives: \[ \text{Area} = \frac{1}{2} \left| -\frac{169}{60} \right| = \frac{169}{120}. \] Thus, the exact area of triangle OAB is \(\boxed{\frac{169}{120}}\).

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